1. Field of the Invention
The present invention relates to electronic ballasts, and more particularly, to electronic ballasts with the regenerative valley filled power factor correction (RVF PFC) capability. This RVF PFC capability is then further utilized to attain power adjustment capability.
2. Description of the Prior Art
The power factor (PF) is a measure of the power quality as defined by: PF=real power/apparent power=displacement factor*distortion factor=cos φ/√(1+THD^2), where φ is the phase shift between the mains voltage and mains current, and the THD is the total harmonic distortion of the mains current, respectively. From a system standpoint, loss due to the phase shift in a device can be recaptured more economically at a group level to get the averaging benefit, but loss due to the THD prefers to be corrected at the device with a power factor correction (PFC) scheme. Otherwise a very bulky and expensive filter operating at the mains frequency is required along with a risk of power system hazard.
Unfortunately, most of the modern electronic devices operate with a dc source that is rectified and filtered from the mains. The filtering capacitor is commonly referred to as the bus capacitor. It receives charges from the rectified mains at an instant causing severe THD on the mains current.
Electronic ballast inside a compact fluorescent lamp (CFL) also uses solid-state electronic circuitry to provide the proper starting and operating electrical conditions to power one or more fluorescent lamps and more recently HID (High Intensive Discharge) lamps. Because of the higher efficiency of the ballast over the traditional magnetic ballast and the improvement of lamp efficiency by operating at a higher signal frequency, electronic ballast offers higher system efficiency. As a result, the CFL has gained tremendous popularity under the banner of energy savings, while its cost and size structure disallows its integral electronic ballast to be equipped with a PFC in most applications.